Simplify the following expression: $x = \dfrac{5}{r} \div \dfrac{5}{9r}$
Solution: Dividing by an expression is the same as multiplying by its inverse. $x = \dfrac{5}{r} \times \dfrac{9r}{5}$ When multiplying fractions, we multiply the numerators and the denominators. $x = \dfrac{ 5 \times 9r } { r \times 5}$ $x = \dfrac{45r}{5r}$ Simplify: $x = \dfrac{9}{1}$